This invention relates to imaging and, more particularly, to imaging utilizing the imagewise deletion of parallel variable diffraction grating domains in thin layers of nematic liquid crystalline materials having negative dielectric anisotropy.
Liquid crystal diffraction gratings are known. See, for example, Carroll, Journal of Applied Physics, 43, 3 (1972); Greubel and Wolff, Applied Physics Letter, 19, 213 (1971). Variable grating mode domains in nematic liquid crystalline materials as distinguished from the Williams domains were denoted as such by Penz and Ford, Physical Review A, 6, 414 (1972) and studied by Greubel and Wolff. The Greubel and Wolff studies showed that the domains in the variable grating mode were formed in a direction perpendicular to the initial homogeneous alignment of the nematic liquid crystalline material. This alignment is hereinafter referred to as the perpendicular variable grating mode.
U.S. Pat. Nos. 3,758,195 and 3,813,145 to Hedman et al. are directed to information display apparatus utilizing as a diffraction grating, a cell containing a liquid crystalline material. It is believed that, at least in some instances, the diffraction results reported in these patents inherently resulted from a variable grating mode nematic liquid crystalline material having negative dielectric anisotropy but that the long axes of the domains in the variable grating mode were parallel to the initial homogeneous alignment (hereinafter referred to as parallel variable grating mode) rather than perpendicular as reported in the Greubel and Wolff article.
Electro-optical cells and displays having a photoconductor in contact with a layer of liquid crystalline material are known. See, for example, U.S. Pat. No. 3,707,322.
In new and growing areas of technology such as liquid crystal imaging, new methods, apparatus, compositions and articles of manufacture are often discovered for the application of the new technology in a new mode. The present invention relates to a novel method of imaging utilizing the formation and imagewise deletion of parallel variable grating mode domains.